1. Field of the Invention
The present invention relates to a belt type driveline and a rack assist type electric power steering apparatus including the belt type driveline. More particularly, the present invention relates to a belt type driveline and a rack assist type electric power steering apparatus including the belt type driveline, which can increase durability while preventing spinning with no traction of a ball nut and a nut pulley due to a slip between the ball nut and the nut pulley in an operation of a driving belt by driving of a motor, and provide a user with convenient steering by minimizing vibration and noise transferred through a rack bar, the ball nut, the nut pulley, etc., when the rack bar slides while the nut pulley and the ball nut rotate.
2. Description the Prior Art
A general rack assist type electric power steering apparatus includes a steering system connected from a steering wheel to both-side wheels and an auxiliary power mechanism for supplying auxiliary steering power to the steering system.
FIG. 1 is a partial cross-sectional view schematically illustrating a general rack assist type electric power steering apparatus, and FIG. 2 is a cross-sectional view schematically illustrating a belt type driveline in the general rack assist type electric power steering apparatus.
The general rack assist type electric power steering apparatus includes a steering system 100 connected from a steering wheel 105 to both-side wheels 150 and an auxiliary power mechanism 160 for supplying auxiliary steering power to the steering system 100.
The steering system 100 includes a steering shaft 110 of which an upper end is connected to the steering wheel 105 to rotate together with the steering wheel 105 and of which a lower end is connected to a pinion shaft 120 through a pair of universal joints 115. Further, the pinion shaft 120 is connected to a rack bar 155 through a rack-pinion mechanism part 135, and both ends of the rack bar 155 are connected to wheels 150 through a tie rod 140 and a knuckle arm 145.
A pinion gear 125 formed in a lower end of the pinion shaft 120 is engaged with a rack gear 130 formed in one side of an outer peripheral surface of the rack bar 155, so that the rack-pinion mechanism part 135 is formed.
An auxiliary power mechanism 160 includes a torque sensor 117 for sensing steering torque applied to the steering wheel 105 by a driver and outputting an electrical signal proportionate to the sensed steering torque, an Electronic Control Unit (ECU) for generating a control signal based on the electrical signal transferred from the torque sensor 117, a motor 165 for generating auxiliary steering power based on the control signal transferred from the ECU, and a belt type driveline 170 for transferring the auxiliary power generated in the motor 165 to the rack bar 155 through a belt 210.
The belt type driveline 170 includes a motor 165 controlled by the ECU, a motor pulley 205a fixed to a shaft 165a of the motor 165, the belt 210 wound around the motor pulley 205a, a ball nut 220 for supporting the rack bar 155 within a rack housing 200 surrounding the rack bar 155, and a nut pulley 205b coupled to an outer peripheral surface of the ball nut 220.
The ball nut 220 rotates while being engaged with the rack bar 155 through a ball to make the rack bar 155 slide in an inner side of the rack housing 200. A bearing 240 for supporting rotation of the ball nut 220 is mounted in the outer peripheral surface of the ball nut 220.
However, according to the conventional art, the ball nut and the nut pulley spin with no traction due to the generation of a slip, so that efficiency of power transmission is deteriorated and the auxiliary steering power cannot be accurately transferred.
Further, there is a problem in that when the rack bar slides while the ball nut rotates, noise and vibration are generated through the rack bar, the ball nut, the nut pulley, the bearing, the rack housing, and the like, and the vibration and the noise are transferred to other components, thereby causing looseness of fastened components.
Further, the transferred noise and vibration are transferred to a driver together with vibration and noise of the other components, thereby deteriorating smooth steering of the driver.